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The blood test helped identify Alzheimer's patients with up to 86% sensitivity and specificity

Currently, the only conclusive method for diagnosing Alzheimer's is after a patient's death

(CNN)An experimental blood test can accurately diagnose Alzheimer's disease, the most common form of dementia, according to a study published Monday in the journal Proceedings of the National Academy of Sciences. Though still in development, the test may someday be used to diagnose other degenerative brain disorders and even mild cognitive impairment resulting from head injuries.

The researchers say that using the test, they were able to identify Alzheimer's patients with up to 86% sensitivity and specificity. (Sensitivity refers true positives identified by the test, while specificity refers to true negatives.) The test also differentiated Alzheimer's from dementia with Lewy bodies, a related condition, with 90% sensitivity and specificity.

The new test's "accuracy is markedly higher than other tests being developed," said senior study author Francis Martin, a professor in the School of Pharmacy and Biomedical Sciences at the University of Central Lancashire in the United Kingdom. "For such a simple test to be so predictive is very exciting."

That said, he himself was surprised by the accuracy, given that other researchers have not achieved similar results using more sophisticated approaches, Martin wrote in an email.

'Life-changing' diagnosis

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Today, there's only one conclusive test for Alzheimer's diagnosis: a postmortem examination of a patient's brain.

Yet while a patient is alive, doctors diagnose the disease based on a careful evaluation that includes brain scans and in-depth mental testing, according to the website for the Alzheimer's Society, a registered UK charity that funds research.

"Current methods of diagnosing dementia can be slow and expensive, so finding a cheap, quick test that can accurately identify if someone has dementia is a top priority for researchers," said Doug Brown, director of research and development at Alzheimer's Society. The society did not fund the new study, and Brown did not participate as a researcher.

A diagnosis of dementia is life-changing. With early detection, medical interventions have the best chance of slowing the progress of disease, according to the society.

For the study, the researchers enlisted the help of 347 participants with neurodegenerative diseases, plus 202 healthy people serving as a comparison group. Participants ranged in age from 23 to 90. The researchers took blood samples from all the volunteers and analyzed the samples with infrared spectroscopy.

This is "a sensor-based technology that has at its core a diamond," Martin explained. "Light is passed through the diamond and bounces off the surface of the diamond. As it does so, the light interacts with chemical bonds in the sample and these vibrate at a frequency that is detected."

These frequencies reveal the chemical bonds in the blood, which indicate whether the blood contains traces of a neurodegenerative disease -- and, if so, which kind, he wrote.

Using this test, Martin and his colleagues correctly identified early cases of Alzheimer's disease with 80% sensitivity and 74% specificity and later stages of the disease with up to 86% sensitivity and specificity when using other patient data.

Beyond a clinic or laboratory's initial outlay for instrumentation, equating to about $50,000 -- "not much really" -- recurrent costs for individual patient tests would be "negligible," Martin noted.

Everyday people and athletes, too

For people with signs of mild cognitive impairment, the test could help doctors "monitor disease progression, tailor treatment based on disease classification and predict progression," Martin said.

Not only would the general public benefit from this test, Martin said, it could be used as a post-injury diagnosis for athletes, including football players and boxers.

"We have now gone well beyond pilot studies," Martin said of the new test. "The appropriate validation studies are next -- these will take five to 10 years."

Brown agreed that more time and study are necessary before the new test can be used by doctors.

"The accuracy is not yet high enough and would currently lead to mis-diagnoses," he wrote in an email. "More development is needed to improve the accuracy before the test could reach the clinic." More study is also need "to ensure these results can be reproduced and replicated."

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"Along with detecting dementia early, this approach has the potential to differentiate between different types of dementia," he wrote, adding that the study is not unique.

"Blood tests are being widely investigated as a potential way to identify people with dementia," Brown wrote. "Alzheimer's Society is also funding studies that identify a wide range of biological signals through cerebrospinal fluid, brain scans and saliva to better detect who is at risk of developing dementia."